A word that Paul Romer used in a recent piece in the Papers and Proceedings of the AER. Its inspired, no doubt, by Stephen Colbert’s notion of `truthiness’. Romer defines it as

Like mathematical theory, mathiness uses a mixture of words and symbols, but instead of making tight links, it leaves ample room for slippage between statements in natural versus formal language and between statements with theoretical as opposed to empirical content.

Romer is not the first to coin the term. Credit goes, I think, to Jordan Ellenberg. Ellenberg defined it as

…..a series of fervent gestures that gives the impression that mathematical ideas are being expressed, but doesn’t actually deliver the goods.